1. Field of the Invention
The present invention relates to a manufacturing method of a magnetoresistive effect (MR) sensor using a giant magnetoresistive effect (GMR) or a tunneling magnetoresistive effect (TMR), and to a manufacturing method of a thin-film magnetic head with the MR sensor, used for a magnetic recording and reproducing unit such as an HDD (Hard Disk Drive) unit or FDD (Floppy Disk Drive) unit for example.
2. Description of the Related Art
Recently, thin-film magnetic heads with MR sensors based on a spin valve effect (SV) of GMR characteristics have been proposed in order to satisfy the requirement for ever increasing data storage densities in today's magnetic storage systems, such as HDD units. The spin valve MR (SVMR) sensor includes first and second thin-film layers of a ferromagnetic material separated by a thin-film layer of non-magnetic metallic material, and an adjacent layer of anti-ferromagnetic material is formed in physical contact with the second ferromagnetic layer to provide an exchange bias magnetic field by exchange coupling at the interface of the layers. The magnetization direction in the second ferromagnetic layer is constrained or maintained by the exchange coupling, hereinafter the second layer is called a “pinned layer”. On the other hand, the magnetization direction of the first ferromagnetic layer is free to rotate in response to an externally applied magnetic field, hereinafter the first layer is called a “free layer”. The direction of the magnetization in the free layer changes between parallel and anti-parallel against the direction of the magnetization in the pinned layer, and hence the magneto-resistance greatly changes and giant magneto-resistance characteristics are obtained.
The output characteristic of the SVMR sensor depends upon the angular difference of magnetization between the free and the pinned ferromagnetic layers. The direction of the magnetization of the free layer is free to rotate in accordance with a leakage magnetic field from a magnetic recording medium. That of the pinned layer is fixed to a specific direction (called as “pinned direction”) by the exchange coupling between this layer and adjacently formed anti-ferromagnetic layer.
Such an SVMR sensor with a typical structure can attain an MR ratio of up to about 2–6%. The MR ratio MR is given from,MR(%)=100×ΔRs(Ω/□)/Rs(Ω/□),where Rs indicates a sheet resistance and ΔRs indicates a change in the resistance.
A synthetic SVMR sensor having a multi-layered pinned structure with a nonmagnetic layer sandwiched by two ferromagnetic layers may attain a higher MR ratio than the typical structure SVMR sensor. However, even in case of such synthetic SVMR sensor, it is impossible to attain an MR ratio of more than 10%.
According to the typical structure SVMR sensor and the synthetic SVMR sensor, an MR ratio attained is very low and also a variation of the sensor characteristics performance will increase because a large ferromagnetic coupling between a pinned layer and a free layer (Hin). It is desired that Hin is substantially zero in order to improve the sensitivity of the sensor and to easily adjust an asymmetrical characteristics of the sensor.
U.S. Pat. No. 6,348,274 B1 discloses an MR element including a pinned layer with two ferromagnetic layers and a nonmetallic multi-layered structure formed by exposure to an atmosphere containing oxygen, nitride or fluorine and sandwiched between the two ferromagnetic layers to improve an MR exchanging rate.
According to this MR element disclosed in U.S. Pat. No. 6,348,274 B1, because it is necessary to form the nonmetallic multi-layered structure of different materials in the pinned layer, the structure itself and also its manufacturing process become complicated. Further, there is no consideration for lowering Hin.
W. F. Egelhoff et al, “Oxygen as a surfactant in the growth of giant magnetoresistance spin valves” J. Appl. Phys. 82(12) pp. 6142–6151 (1997) discloses a bottom type SVMR sensor including an anti-ferromagnetic layer made of NiO, a pinned layer, a free layer and a nonmagnetic metallic layer sandwiched between the pinned layer and the free layer. One surface of the nonmagnetic metallic layer was exposed to oxygen so as to reduce a ferromagnetic coupling (Hin) between the pinned layer and the free layer.
In accordance with this SVMR sensor, although Hin can be reduced, it is impossible to improve the MR ratio.